The present invention relates to an evaporator for a heating, ventilating and air-conditioning system in general, and more specifically to an evaporator having multiple fluid paths.
Evaporators in general are well known in various configurations for routing a refrigerant through a plurality of tubes to absorb heat or thermal energy from air passing around the tubes. The cooled air is then directed to an enclosure such as a vehicle for the comfort of individuals therein. In general, a refrigerant medium is routed to an input tank whereupon the refrigerant is further routed through a plurality of tubes to an outlet tank for return back to a compressor. The tubes through which the refrigerant flows are arranged so that the airflow to be cooled passes in proximity to the tubes and contacts a large surface area of the tubes. These arrangements typically also include multiple air fins arranged axially with the airflow and extending between adjacent tubes thereby increasing the contact surface area to aid in the transfer of heat from the air to the circulating refrigerant. The refrigerant is continuously circulated in a closed loop fashion for continuous cooling of air flowing through the evaporator.
To obtain the maximum heat transfer from the air to the refrigerant, the refrigerant is routed to make multiple passes through the air stream to be cooled prior to being discharged from the evaporator for recirculation. As the refrigerant makes each individual pass through the air stream and absorbs more thermal energy, its cooling capacity decreases. Therefore, the portion of the airflow through the tubes carrying the initial pass of the refrigerant is cooled to a greater extent than the air passing farther downstream of the refrigerant flow. This results in an undesirable non-uniform discharge air temperature.
The problem of non-uniform discharge air temperatures in HVAC modules may be traced, at least partially, to imperfect evaporator core designs. Current evaporator designs exhibit two significant problems. First, a single core operating under given test conditions provides good cooling capacity but causes a non-uniform outlet air temperature distribution (i.e., a large temperature spread) under certain conditions as a result of non-uniform refrigerant flow in some passes or operation at high superheats. For this reason evaporators incorporating two cores with refrigerant flowing through the cores in series have been constructed within the same core depth as a single core. Although this design provides a more desirable temperature spread, the desirable temperature spread is obtained at the expense of cooling capacity. The degradation in the associated cooling performance is a result of the severe refrigerant pressure drop in the system.
The general construction of a dual core evaporator is well known in the art and generally comprises an upstream core through which the air to be cooled passes first and a downstream core immediately downstream and adjacent to the upstream core. The air exiting the upstream core immediately enters the downstream core for additional cooling. Each core has an upper tank and a lower tank with a plurality of tubes extending between the two tanks wherein the adjacent tubes have multiple cooling fins extending from one to the other. The refrigerant makes multiple passes through successive groups of tubes in the upstream core and is then routed to the downstream core where the refrigerant makes multiple passes through like but opposite successive tube groups and then exits the evaporator.
Other configurations of evaporators employ a xe2x80x9cUxe2x80x9d flow wherein the refrigerant enters an upstream core and is first routed through one group of tubes and then to the corresponding group of tubes in the downstream core. The refrigerant flows span wise down the evaporator to the next group of tubes whereupon the refrigerant flows through the downstream group and is then transferred to the corresponding upstream group of tubes and so on. The refrigerant flow finally ends at an end of the evaporator opposite from the inlet. Since it is desirable to have the evaporator inlet and outlet at the same side of the evaporator the xe2x80x9cUxe2x80x9d flow designs also incorporate an additional tank to route the refrigerant back to the end of the evaporator at which the refrigerant entered. However, none of the current designs, either single core or multi-core, provide optimization of both a uniform outlet air temperature distribution and cooling capacity.
Thus, there is a need for an HVAC evaporator that exhibits both a high efficiency and a uniform outlet air temperature distribution.
In one aspect, the present invention includes an evaporator for an HVAC system wherein an upstream to downstream airflow is directed through the evaporator for inducing a transfer of thermal energy between the airflow and a fluid circulating in the evaporator. The evaporator includes at least two cores adjacent one to the other. Each of the cores defines a core inlet and a core outlet and the cores are arranged such that the core inlet of the first core is positioned at an opposite end from the inlet of the second core. Correspondingly, the outlet of the first core is positioned at an opposite end from the outlet of the second core. The evaporator inlet is in fluid communication with the first core inlet and the second core inlet and the outlet is in fluid communication with the first core outlet and the second core outlet.
Another aspect of the present invention includes an evaporator for an HVAC system of the type wherein an upstream to downstream airflow is directed through the evaporator for inducing a transfer of thermal energy between the airflow and a fluid circulating in the evaporator. The evaporator includes a plurality of tube plates each plate having a face and a back. The plurality of tube plates are arranged in alternating fashion, face-to-face, back-to-back, and define at a top portion thereof a top upstream tank and a top downstream tank. The two plates further define at a bottom portion thereof a bottom upstream tank and a bottom downstream tank. Each of the tanks substantially extend from a first end of the evaporator to a second end of the evaporator. Each of the back-to-back arranged pairs of tube plates also define an upstream tube extending from the top upstream tank to the bottom upstream tank wherein the tube is in fluid communication with the tanks for permitting a fluid flow between the top upstream tank and the bottom upstream tank. The back-to-back arranged pairs of tube plates further define a downstream tube extending from the top downstream tank to the bottom downstream tank and in fluid communication therewith for permitting a fluid flow between the top downstream tank and the bottom downstream tank. A first endplate at the first end of the evaporator defines an input in fluid communication with one of the upstream tanks at the first end of the evaporator and with one of the downstream tanks at a second end of the evaporator. The first endplate further defines an output in fluid communication with a second of the upstream tanks at the second end of the evaporator and with a second of the downstream tanks at the first end of the evaporator. A second endplate is positioned at the second end of the evaporator.
Yet another aspect of the present invention is a method of transferring a thermal transfer fluid flow through an evaporator of an HVAC system of the type having an upstream core including a plurality of thermal transfer tubes and a downstream core including a plurality of thermal transfer tubes and an inlet and an outlet wherein the method comprises the steps of inputting the thermal transfer fluid flow into the inlet and then splitting the thermal transfer fluid flow to an upstream flow and a downstream flow. The upstream flow is then directed through the upstream core from a first end of the evaporator to a second end of the evaporator, and the downstream flow is directed through the downstream core from the second end of the evaporator to the first end of the evaporator. The upstream flow and downstream flow are combined at the outlet and the fluid flow is then output from the outlet.